[StarCMC]

There are rules as to whom the Geneva convention applies. The insurgents are not among those covered for more than one reason. Read it here.

The appropriate portion is here (emphasis mine):

Article 4

A. Prisoners of war, in the sense of the present Convention, are persons belonging to one of the following categories, who have fallen into the power of the enemy:

1. Members of the armed forces of a Party to the conflict as well as members of militias or volunteer corps forming part of such armed forces.

2. Members of other militias and members of other volunteer corps, including those of organized resistance movements, belonging to a Party to the conflict and operating in or outside their own territory, even if this territory is occupied, provided that such militias or volunteer corps, including such organized resistance movements, fulfil the following conditions:

(a) That of being commanded by a person responsible for his subordinates;

(b) That of having a fixed distinctive sign recognizable at a distance; (c) That of carrying arms openly;

(d) That of conducting their operations in accordance with the laws and customs of war.

3. Members of regular armed forces who profess allegiance to a government or an authority not recognized by the Detaining Power.

4. Persons who accompany the armed forces without actually being members thereof, such as civilian members of military aircraft crews, war correspondents, supply contractors, members of labour units or of services responsible for the welfare of the armed forces, provided that they have received authorization from the armed forces which they accompany, who shall provide them for that purpose with an identity card similar to the annexed model.

5. Members of crews, including masters, pilots and apprentices, of the merchant marine and the crews of civil aircraft of the Parties to the conflict, who do not benefit by more favourable treatment under any other provisions of international law.

6. Inhabitants of a non-occupied territory, who on the approach of the enemy spontaneously take up arms to resist the invading forces, without having had time to form themselves into regular armed units, provided they carry arms openly and respect the laws and customs of war.

[ordinaryguy]

There are rules as to whom the Geneva convention applies. The insurgents are not among those covered for more than one reason.

The quoted article defines the term "Prisoner of war". I'm not finding any language in that article which declares the absence of uniforms to be a war crime.

Given that the excerpt is part of the 'Geneva Convention relative to the Treatment of Prisoners of War', I wouldn't expect it touch upon that topic.

[Alberta's Child]

I can tell you from my own first-hand knowledge that some number of "U.S. security contractors" operating in both Afghanistan and Iraq would not be considered lawful combatants, either.